Most of blast furnace slag, convertor slag and electric furnace slag or the like produced in the processes of iron manufacture and steel manufacture had been disposed by throwing away. However, in recent years because of decrease of reclaimable land and in view of effective utilization of resources, recovery of an iron content from slag and reuse of the slag for aggregate etc. have been practiced.
For such a reason, the applicant has developed a swingable type crushing apparatus. This apparatus enables effectively crushing or deforming the massive furnace slag containing iron whose ratio is as high as more than 50-60% and its dimension is larger than 300-500 mm as disclosed in U.S. Pat. No. 4,637,562. By providing a hydraulic mechanism to this swingable type crushing apparatus, during operation of the crushing or deformation of the massive furnace slag, the movement of the apparatus becomes smooth and an excessive load is not applied on a respective portion of the apparatus, thereby enabling improvement of the function of the apparatus.
In the conventional control method for the above-mentioned swingable type crushing apparatus, when the crushing or deformation of the massive furnace slag is conducted in ordinary operation, compressive force is applied to a swingable crushing plate and in such a condition that a hydraulic pressure is produced in a hydraulic line of a hydraulic mechanism. When the compressive force is less than a maximum supplying pressure of the hydraulic line the operation of the crushing or deformation of the slag is continued, and when the compression force is greater than the maximum of supplying pressure of the hydraulic line the swingable type crushing plate is moved backwardly to increase the crushing clearance under the condition of compressing the massive furnace slag, and the crushing is accomplished and the slag is discharged through an outlet of the crushing chamber.
However, because of the properties and the configuration of the massive furnace slag, even if the normal swing motion is given to the swingable crushing plate, there are occasions that biting effect by the crushing plate against the massive furnace slag within the crushing chamber is not enough to apply appropriate compressing force on the slag. Upon the operation of the apparatus under such crushing circumstances, the contacting locations between the massive furnace slag and the crushing plate in the crushing chamber is changed in such a manner that the crushing clearance is increased or decreased stepwisely to ensure the appropriate biting against the massive furnace slag, so that under the activation of sufficient compressive force the crushing is carried out and finally the crushed slag is discharged through the outlet of the crushing chamber.
At this time, the increasing and the decreasing of the crushing clearance are varied at a ratio of 1/10-1/5 of initial set value, and the massive furnace slag is successively crushed without shutdown of the operation of the swingable type crushing apparatus (disclosed in the aforementioned U.S. Pat. No. 4,637,562).
However, in the above-mentioned method for controlling the operation of the swingable type crushing apparatus, there are problems in monitoring variation in the crushing condition due to the configuration and the properties of the massive furnace slag and also due to tendency of fluctuation of hydraulic pressure in a hydraulic mechanism due to applied compressive force, Furthermore adjustment of the crushing clearance of the swingable type crushing mechanism by increasing or decreasing it stepwisely for controlling operation of the apparatus can not be readily effected.
Especially, after supplying the massive furnace slag into the crushing chamber, when a bridging or adhering phenomenon happens within the crushing chamber between the furnace slag masses in mutual or between the crushing plate and the massive furnace slag, even if hydraulic signals of the hydraulic mechanism exhibit a non-loading condition, the massive furnace slag might still remain in the crushing chamber, and thus the crushing condition of the massive furnace slag is impossible to be monitored correctly.